Printing plates may be imaged on a plate making machine and then transferred to a printing press. Once on the printing press, the images from the printing plates are transferred to paper or other suitable substrates. It is important that images printed using a printing press be properly aligned with the substrate on which they are printed. Obtaining such alignment typically involves:                carefully aligning a reference edge of a printing plate with pins or other features on the plate making machine;        detecting one reference point on an orthogonal edge of the printing plate (i.e. orthogonal to the reference edge) at a known distance from the reference pins;        imaging the printing plate; and,        using the reference edge and the orthogonal edge reference point to align the printing plate on a drum of the printing press.One common technique of aligning the printing plate on the drum of a printing press involves using the reference edge and the orthogonal edge reference point to align the printing plate on a punching machine and punching registration holes in the printing plate. The printing plate may then be aligned on the drum of the printing press with registration pins which project through the registration holes.        
Printing plates are typically rectangular in shape. One of the long edges of the printing plate is typically used as a reference edge.
In the printing industry there is a general need for ways to improve the speed and accuracy with which printing plates can be prepared.